1. Field of the Invention
This invention relates to the handling of tobacco materials, and more particularly concerns apparatus for separating pieces of tobacco lamina material from heavier tobacco stem material.
2. Description of the Prior Art
In the production of cigarettes, dried and cured whole tobacco leaves are subjected to a threshing operation which fragments the leaf into a mixture of leafy or lamina pieces, and heavier pieces referred to as stem or midrib material. The lamina pieces, which are of thin, filmy configuration, represent the valuable component for use in the production of cigarettes. The stem material, generally of elongated and relatively thick configuration is relatively undesirable for use in cigarette production. It is therefore sought to separate the lamina material from the stem material.
In general, devices employing air currents to separate tobacco lamina from stem material are well know. Examples of such devices include those disclosed in U.S. Pat. No. 4,454,194 to Coleman, U.S. Pat. No. 3,608,716 to Rowell, and U.S. Pat. No. 3,265,210 to Haite et al. In such separator devices, a threshed mixture is entered into a chamber where it is acted upon by an upward flow of air. The aerodynamically lighter lamina pieces are carried upwardly by the air current whereas the heavier stem material falls to a lowermost region of the chamber.
In practice, the upwardly delivered pieces of lamina are removed from the chamber and forwarded toward the next step in the manufacture of cigarettes or other tobacco products. The heavy stem material, however, is forwarded to the entrance port of a next successive downstream separator or thresher, the reason being to glean any residual fragments of valuable lamina material from the stem material. It is not uncommon for the stem material to pass sequentially through a series of four or five separators in a linear arrangement. Several such lines of separators are customarily utilized in typical factory installations.
The considerable floor space occupied by the arrays of separators translates to increased manufacturing expense. The separators further produce a significant problem of air-borne dust in the factory environment. Noise level is a further problem. The energy requirements of the separators is a significant factor, especially the amount of energy required in transporting the heavy stem material. The installation of an array of separators usually involves significant expense for ancillary or support features such as means for supplying the necessary air flow, and means for delivering stems exiting one separator to the entrance of the next separator.
A particularly challenging problem in the operation of pneumatic tobacco separators is to secure efficient utilization of the working air stream. In order to achieve the desired separation of components, the tobacco mixture must be contacted within a confining chamber by an upwardly directed laminar flow of air of substantially uniform velocity throughout the chamber. The chambers are generally of large volume and laterally elongated. Air supply conduits, however, are generally of circular contour, having a cross-section area much smaller than that of the chamber. Difficulties are consequently encountered in causing the air flow from a small conduit to spread out to provide a laminar flow pattern of uniform velocity throughout the chamber.
It is accordingly an object of the present invention to provide apparatus for pneumatically separating a threshed tobacco mixture into stem and lamina fractions.
It is further object of this invention to provide separator apparatus as in the foregoing object which occupies relatively little floor space and readily interacts with other similar separators in a linear array.
It is another object of the present invention to provide a separator of the aforesaid nature which minimizes production of air-borne dust in the adjacent environment.
It is a still further object of this invention to provide a separator of the aforesaid nature which requires reduced energy consumption and permits lower installation cost.
It is yet another object of the present invention to provide a separator of the aforesaid nature which provides improved efficiency of utilization of an activating air stream.
These and other beneficial objects and advantages will be apparent from the following description.